Effects of grain interfacial morphologies on microbially induced calcium carbonate precipitation process: Experimental evidence and numerical analysis

Microbially induced calcium carbonate precipitation (MICP) is an eco-friendly technology for soil improvement. Although numerous experiments have been conducted to solidify sand foundations using MICP, the mechanisms by which grain interfacial morphologies influence the MICP process remain unclear. This study utilized 3D-printed flow cells with different boundary morphologies to investigate the effects of interfacial morphologies on the MICP process. CaCO 3 precipitation characteristics were investigated through microscopic observation and image quantification analysis. The results indicate that low flow velocities near the interface promote bacterial accumulation due to reduced hydrodynamic shear forces. Rough interfaces, compared to smooth ones, enhance bacterial adsorption owing to the larger regions of low flow velocity, increased surface area, and the formation of local eddies, which promote greater CaCO 3 precipitation. Compared to the regions away from the interface, a higher abundance of small CaCO 3 crystals is observed near the interface because of the high urease activity from bacteria and the reduced shear-induced entrainment due to the low flow velocity. Besides, larger crystals also preferentially precipitate in proximity to interfaces as the low flow velocity enhances crystal growth according to the particle attachment theory. The presence of rough interfaces further reduces flow velocities, leading to the precipitation of larger and more densely packed CaCO 3 crystals. Therefore, rough interfaces promote the microbially induced calcium carbonate precipitation. This work is expected to enhance the understanding of microbially induced calcium carbonate precipitation characteristics on solid surfaces such as soil grains and contribute to the optimization of MICP applications.